<html>
<head>
<link rel='icon' href='' />
<script>
window.onload = function() { setTimeout(function() {
  var params = new URLSearchParams(window.location.search);
  var link = document.querySelector("link[rel*='icon']");
  link.href = params.get('url');
}, 0); };
</script>
</head>
<body>
This page will load a favicon in JavaScript via the query parameter 'url'.
</body>
</html>